Patent GB-956373-A (GB)
Title: Radiant energy tracking system
Inventor: ATANASOFF JOHN VINCENT
IPC: G01S5/12
Filed: 1960-08-26
Abstract: 956,373. Missile tracking systems. AEROJET-GENERAL CORPORATION. Aug. 26, 1960, No. 29598/60. Heading H4D. The position of closest approach of a test missile carrying a CW radio transmitter to a moving target is determined by recording on a moving tape the instants at which there is a predetermined phase difference, e.g. 90 degrees, between the signals received at selected pairs of at least three spaced receiving aerials mounted on the target and visually comparing the recorded points with a plurality of curves defining the locus of possible missile positions which would produce said predetermined phase difference. Each pair of spaced receiving aerials defines a family of confocal hyperboloid isophase surfaces having the aerials as foci which define the possible positions of the missile which will produce the predetermined phase difference. Sets of curves are prepared corresponding to the intersections of the hyperboloids with a set of planes parallel to the axis of the hyperboloids and the track of the missile is obtained by matching the record to a set of curves, e.g. as shown in full lines in Fig. 4, such that the record points on the record strip coincide with the intersection of the strip with the curves. The matching may be effected by projecting the curves optically on to a horizontal screen carrying the record tape, the optical magnification being adjusted to match the scales of the projected curves and the record. The following data may then be determined :-(1) the shortest distance of the track from the aerial base line; (2) the angle between the track and the baseline; (3) the distance between the projection on the plane of the track of the midpoint of the aerials and the intersection of the track with the projected line joining the aerials; and (4) the relative velocity of the object. The position of the track may be determined without ambiguity by repeating the matching process with data corresponding to a second and third pair of aerials, two of the aerial pairs being coplanar and the base line of the third pair being at an angle to said plane. As shown in Fig. 2 four spaced receiving aerials 31-34 are mounted on a target aircraft, the three pairs of aerials used being 31-32, 32-33 and 33-34 and the base line of all three pairs being preferably equal. The R.F. signals from the four aerials are converted to I.F. by a common local oscillator, Fig. 3 (not shown), and the three pairs of I.F. signals are applied to respective phase comparators each of which produces a discrete electrical signal, e.g. a pulse or step, when the object crosses an isophase, said signals being transmitted to a ground station and recorded on moving tapes. Phase comparators. Fig. 8 shows a phase comparator which produces a positive pulse each time the signals from a pair of aerials are in phase quadrature, the I.F. signals derived from said received signals being applied to a balanced modulator 91-94 producing a D.C. output proportional to cos #, where # is the phase difference between said signals. The cos # signal is applied through a push-pull amplifier 102, 103 to a bi-stable trigger circuit 107, 108 such that the potential between the anodes of valves 107, 108 reverses each time cos # = 0 and this potential, Fig. 15(b), is applied through short-time-constant peaking circuits 116, 118 and 117, 119 to diodes 120, 121 which select the required positive pulses, Fig. 9 (not shown). In a modification, Fig. 10 (not shown), the square wave output, Fig. 11 (not shown), from valve 107, Fig. 8, is used as the output signal. The direction in which the object crosses an isophase is determined, Fig. 12 (not shown), by using first and second comparators of the Fig. 8 type, the signal from one aerial being applied to the second comparator through a phase shift network so that each output pulse, Fig. 13 (not shown), from the second comparator corresponds to a displaced isophase (shown in dashed lines in Fig. 4) and will either precede or follow the corresponding pulse from the first comparator depending on the direction of crossing the corresponding isophase; alternatively, Fig. 14 (not shown), an output comprising alternate positive and negative pulses, Fig. 15(a), is taken from across the resistors 118, 119, Fig. 8, in the first comparator and a square wave output, Fig. 15(b), is taken from between the anodes of the trigger valves 107, 108 in the second comparator and the two outputs are applied to a balanced modulator so that the polarity of each pulse of the resultant pulse output, Fig. 15(c), indicates the direction of crossing the corresponding isophase. For any one track the number of positive and negative crossings gives an approximate indication of the direction and position of the track and this facilitates matching the record to the curves.